The present invention is directed to a bicycle crank axle, a crank arm, and a crank set that offer high mounting precision and fastening strength, and that contribute to lighter weight. It also relates to a bolt and assembly tools used for assembling these components.
In conventional mounting mechanisms for the crank arms and crank axle in a bicycle, both ends of the crank axle are shaped into essentially square columns, a square hole is made in each crank arm, and the two are fitted together to fasten the crank arm onto the axle. The precision of centering afforded by the conventional mechanism for fitting together the crank arms and the crank axle is inadequate, and the strength of the linkage in the direction of rotation is inadequate as well. The problem of inadequate linkage strength is particularly notable where an aluminum alloy hollow pipe structure has been adopted for the crank axle, or where an aluminum alloy hollow structure has been adopted for the crank arms in order to reduce weight.